【作者】 初丽娜；

【导师】 龚学庆；

【作者基本信息】 华东理工大学 ， 工业催化， 2011， 硕士

【摘要】 本文采用基于密度泛函理论的理论计算方法,在原子尺度上研究了有关有机小分子在氧化物表面的吸附及迁移机理。首先,研究了邻苯二酚在含不同羟基含量的金红石TiO2(110)表面的各种迁移机理。TiO2(110)表面羟基化程度是邻苯二酚在表面迁移的关键。其解离吸附的分子的迁移只可能发生在含羟基的表面。室温下只有Hydrogenated Rotation机理是可行的,解离的邻苯二酚通过重新获得并再次释放H在表面进行迁移。然而,过度羟基化的表面会使迁移速度再次降低。该项研究成果对于从根本上认识氧化物表面吸附分子的动力学特征,实现调控材料表面性质,特别是二氧化钛等半导体材料的表面光催化性能具有十分重要的意义。其次,研究了乙酸在金红石TiO2(110)和(011)-2×1表面的解离吸附构型和迁移机理。室温下乙酸在TiO2(011)-2×1表面的初始吸附只发生在有缺陷处。当表面覆盖度较高时,形成准一维乙酸团簇。预先吸附的乙酸对后续乙酸的吸附影响很大。与Ti02(110)表面的双齿桥式吸附构型相比,乙酸在TiO2(011)-2×1表面最可能形成的是单齿吸附构型。室温下,乙酸在TiO2(110)表面的吸附是随机的,遵循Langmuirian吸附规律,而在(011)-2×1表面的吸附是以预先吸附的乙酸为团簇成核中心。此外,乙酸在金红石TiO2(110)表面的迁移,室温下只有经过一个双齿螯合中间态的Diffusion机理是可行的。表明分子构型的差异会影响分子在表面的迁移方式,以及表面羟基组位点的不同会影响分子迁移的势垒。更多还原

【Abstract】 We studied adsorption and diffusion of organic molecules on oxide surfaces by destiny functional theory (DFT).We investigated the diffusion behavior of catechol on the rutile TiO2(110) surfaces under different conditions. It has been found that the degree of hydroxylation of the surface is essential for the facile diffusion of catechol at the surface. The diffusion of catecholate adsorbed on Ti02(110) surface can be possible only with the existence of surface hydroxyls. The so-called Hydrogenated Rotation Route is energetically the most feasible at room temperature, where the transfer of hydrogen from surface hydroxyls to the molecule and its interaction with surface hydroxyls substantially lowered the activation barrier for rotational motion across the surface. However, a heavily hydroxylated surface is not favorable to the diffusion of catechol. This work illustrates the essential role of hydrogen bonding in controlling dynamics during the initial stage of molecular assembly.We also investigated the adsorption behavior of acetic acid on the rutile Ti02(110) and (011)-2×1 surfaces, and the diffusion at TiO2(110) surface. DFT calculations showed that the initial sticking of adsorbed acetic acid at room temperature is low on the (011)-2×1 surface with initial chemisorption occurring at surface defects only, and for high acetic acid exposures we determined adsorption of quasi-one dimensional ordered acetate-clusters. Pre-adsorbed acetates act as nuclei for further adsorption, causing the formation of acetate islands. Furthermore, only monodendate adsorption is possible for the acetate in the clusters on TiO2(011)-2×1 surface, very different from the established bidentate bridging adsorption on TiO2(110). At room temperature, the adsorption kinetics on the (110) surface is randomly at low coverage and follows a Langmuirian adsorption, and adsorbed acetate arrange in an ordered 2×1 superstructure at saturation coverage. While on the (011)-2×1 surface acetate adsorbs to pre-adsorbed molecules in an island growth mechanism. Moreover, the most feasible diffusion route of acetic acid across TiO2(110) shows that the catecholate assumes a bidentate chelating intermediate state. Calculation results indicate that different molecular configurations can critically influence the way of diffusive motion, and different sites of the surface hydroxyl groups will affect the diffusion barrier.更多还原